1. Field of the Invention
The present invention relates to an ultrasonic motor, and particularly relates to a linear driving type of ultrasonic motor (hereafter referred to as linear ultrasonic motor).
2. Description of the Related Art
In a linear ultrasonic motor, conventionally, a high-frequency voltage is applied to a piezoelectric element, and thereby the piezoelectric element vibrates a fixed ultrasonic vibrator. The vibration of the ultrasonic vibrator drives a sliding member which is pressurized by the ultrasonic vibrator. Various ideas are considered for achieving a linear ultrasonic motor which can keep a high output even with a small size and enhances driving efficiency.
For instance, in a linear ultrasonic motor disclosed in Japanese Patent Application Laid-Open No. 2005-99549, a transmission unit between an ultrasonic vibrator and a member to be driven is arranged in a direction perpendicular to an optical axis, in other words, perpendicularly to a driving direction.
However, in the above described linear ultrasonic motor disclosed in Japanese Patent Application Laid-Open No. 2005-99549, it has been necessary to increase a pressurization force of a bias member against a vibrator, in order to prevent a follow-up delay in the driving direction. However, there has been a problem that when the pressurization force is excessively large, an equalizing property for a transmission member decreases.
An object of the present invention is to provide a linear ultrasonic motor which can efficiently transmit a driving force to a body to be driven.